Many really good comments. I would also look at another angle with the OP (and none of this is meant to be antagonizing at all, Sir). I would ask rhetorically what the rest of your lifestyle looks like. Are you physically in shape? Mentally alright other than the work part? Do you eat well? McDonalds and Taco Bell, or packing healthier stuff? Got good kicks on your dogs? What's your alcohol intake look like - none, daily, weekly, excessive, one here or there? What's your sugar intake look like - water, soda, beer, all of the above? How much? When? Are you sleeping? How much? These are just a few of the small things that can take a toll.... slowly.
Might sound stupid to some or many, but a lot of those things play a role in how your days go.